You can still have rocky islands if you want. The presence of vegetation on an island mostly depends on the availability of fresh water, which has a lot to do with rain and soil. Being cold or hot isn’t as much of a factor. If the islands are solid rock and get little rain, they’ll have little growing on them.
Geysers are not a good way to warm up a whole environment. Long before you changed the ambient temperature, you’d kill everything off with excess hydrogen sulfide and sulfuric acid (among other nasty emissions). If you do want some kind of barren wasteland and it doesn’t have to be a desert, you could simply ascribe it to poisoning by volcanic emissions.
You say that you’re assuming T-Rex is cold blooded, but there’s not much agreement on that point. If dinosaurs really are the ancestors of birds, then at least some were warm-blooded. Cold-blooded or not, if you see T-Rex as an active hunter (rather than a wait-and-ambush predator like a croc or a snake), then they’re going to have a high metabolism. It takes a lot of energy to keep a 7-ton creature moving.
In reference to Titanosaurs… I would not go so far as to say they’re impossible. I’d stick with the math on the food pyramid principle. However, I do think Blake brings up good points about competition. Just because an environment is able to supply enough food for a herd of hadrosaurs and a herd of titanosaurs does not mean that you can sustain both. If the entire environment is homogenous, then one of them is better adapted to it. Perhaps hadrosaurs breed faster, out-compete titanosaurs for food, and take over. Perhaps titanosaurs can’t be killed by predators, so the hadrosaurs dwindle over time while titanosaurs take over. (Which would be disastrous, because then they’d overgraze and the population would crash).
If you’re going to have both, they need niches that justify why they are alive, and why they are alive in the numbers you’re talking about.
Alright. What if I go the Lost World route? Deadly disease wipes out nearly all titanosaurs after they reach reproductive age, but before they reach full size?
Meh. That would be plagiarism. And I want a natural environment.
So how big of an animal can I have? Brachiosaurus is probably too big… Diploducus?
But the reason that forest doesn’t spread into savanna is because of fire. And the reason that fires are able to mainatain a savanna is because of the prolonged annual dry season and the continuous herbaceous understorey. So we’re right back where we started with a system that needs to be seasonally dry with an open canopy and herb layer.
I’m not quite sure what you’re trying to achieve with this system, but if you let us know I’m sure we can come up with something plausible that works in reality. You certainly can get rapid transitions from rainforest to savanna systems under the right conditions if that is what you want. And you can also get grassland systems with high annual porductivity.
dracoi pretty wel covered why thisis a non starter.
Once again, if you tell us why you need these specific climatic distiruibutions we can probably help you. But I don’t see why it’s so important to have the driest areas adjacent to the coast, rather than further inland.
Tall grasses are the typical vegeation that dominates in such a sitaution. Grasses didn’t really exist in the time of the dinos so stoloniferous ferns presumably filled a similar niche. Bamboo however has all the same problems as other woody plants in that it needs to invest a lot of energy into producing woody biomass that is destroyed regularly.
All things being eqqual any temperate system will be less productibve than any tropical system. There is simply less energy avialable. Tropical herblands are still your best bet.
It doens’t matter how you shake them up, if an area can support one tonne per ten hectares then that’s its maximum productivity. And that’s being highly optimistic. On natural grassland the sustainable stocking rate of cattle tops out at about a beast/4ha or around one tonne/10 ha. And that’s with modern medicine, zero predation, artificial watering points, predator control, elimination of virtually all competetion from locusts, groundhogs, deer etc. In the natural world you could probably expect 1/100th of that population density.
Whether the animals are one huge nomadic herd or lots of smaller sedentray herds won’t make a lot of difference
If we assume a continuous slab of tropical herblands 700km to a side and go for the optimistic figure of 1 tonne/10 hectares then we get 4 ,900, 000 tonnes of animal. Allowing for predation, disease, lack of water etc. that gives you about 49, 000 tonnes of large animal biomass. That’s ~15, 000 x 3 tonne animals. If you allow that a large herd is 500 head that should give you enough to have multiple herdsof several species.
The problem is that these things grow so slowly. Being conservative it wll take them 20 years top reach reproductive maturity. So to have a token population of 200 adults you’ll need to have at least twice that many juveniles, so that’s a minimum 300 animals. And you need to be able to sustain that during the worst drought years because they need at least 20 years to recover any losses to the breeding population. So you’d probaly need a population of 3000 adults and subadults in the good years to sustain a breeding population of 100. Given that your island will only suport 50, 000 tonnes of large animal biomass you’ll end up using it all and more just to support the 100 tonne titanosaurs
This is why large animals generally don’t do well on islands. A herd of 100 goats that is reduced to just 10 individuals in a drought will recover numbers completely within 5 years because the population of females doubles each year. A population of elephants facing the same reduction in numbers will take at least half a century to recover, by which time the next bad season will have further decimated them. Such animals find it tought to recover and gradually fade into extinction.
One option to have a token titanosuar presence may be to play upon the long growth period and lack of parental care. If we postulate a population structure where there are only a maximum of 50 adult females at any time, each laying ~100 eggs each year then >90% of the population could exist as juveniles. When the adult populaton crashes sufficent juveniles will survive to ensure gentic diveristy or if necessray repopulate entirely. That’s a pretty precarious existence for a species and would lead to dwarfing, but it’s possible if you really want to have some smallish brontosaurs hanging around.
That’s true, though it’s debatble if the theropods were cold blooded. Even if we assume they were then T. rex is still at a comeptetive advantage over smaller and equally cold blooded dinos which will also eatless than a comparble sized brid or mammal and also less than the Tyranosaur.
Essentialy you need to be able to explain what advantage large isze is givingto a creature in an environment with a restricted food supply. Large cretaures always eat more and they also recover more slowly from populaton crashes. Those aren’t good things on an island unless the large size gives a big advantage. Usually that advantage comes in the ability to store more food during bad seasons, but if your island has such regular bad seasosn then the carrying capacity is going to be much lower.
Colibri’s covered why it’s tough to have a ground based scavenger. And note that when I said “bear” I meant omnivore, as in eating carrion, fruit, young animals, fish and so forth.
Cheetahs are right out, they’re highly specialised large game predators with no other options. Island predators need to be generalists with a wide range of options.
Any size reduction will be beneficial, but what the cut off point is will be difficult to gauge. Essentially the more options anisland predator has the better off it wil be. So a coyote that can live on rats and carrion in the bad seasons and turn to hunting deer in the good seasons has a huge advatage over a puma that is a specialised large animal hunter that will have difficulty tackling prey smaller than a rabbit. Similarly small, social animals like hyaenas or dogs that can disperse in the bad seasons and pack up to take down large prey in the good seasons have a distinct advantage. For all those reason you’d expect island carnivores to be significantly smaller than their larget prey species, as small as possible while still retaining the abilty to act as facultative predators. So figure your top predator at ~1/10th of the largest major prey species.
Probably continent size. You essentially need a landmass that’s big enough to always have some refugia from catstrophes from which these large predators can repopulate. To give you some idea, tigers seem to have reached many of the SE Asian islands, but the smallest island they sustained themselves on was java, an island of about 150, 000 km^2 or about ¼ the size of Madagascar, and even there they may have repopulated routinely from Sumatra. If we alow that a Tyrannosaurs needs 10 times the area of a tiger then you really are looking at continent sized landmasses.
With a wide shallow sea or lots of lagoons it’s plausible.
Alright. Works for me.
Things haven’t really changed, except that their preferred pant species is going to become extinct. The woody plants that get destroyed but not eaten will either evolve spines or contact poisons to avoid being damaged or else they will be outcompeted by herbaceous plants that recover faster from damage. The plants that are being sort out and eaten will have no chance at all of outcompeting either and they will rapidly become extinct.
What you’re describing is identical to what happens with goat overgrazing. And what inevitably happens is that the palatable woody species are rapidly exterminated and replaced with unplatable woody species and herbaceous species.
That would simply result in dwarfing, since the creatures that matured at the smallest size would have the longest reproductive life.
My SWAG would be that your maximum size limit is around 20 tonnes. Anything larger than that is either going to be eating too much or maturing to slowly to survive.
I wouldn’t because it ‘s based on some seriously flawed assumptions, not least of which is that every single bit of plant material is edible with maximum conversion. Added to that is that it assumes that your grasslands have absolutely no rabbits, tortoises, grasshoppers, termites, slugs or any other herbivores whatsoever aside from your large beasties. It also assumes that your beasties can eat every single gram of the above ground biomass of every species and have absolutely no impact on sustainability. It also assumes that the annual variation is absolutely uniform with no bad seasons. It also assumes no disease, predation or other factors that result in unproductive loss of animal biomass.
In reality at between half and 90% of the biomass is going to be consumed by small consumers.
Then between 10 and 60% of what remains is going to unavilable because it is unpalatable, toxic or with poor conversion rations. In additon another 25% has to be set aside as reserve so you don’t flog out the pasture. The less you set your reserve as the higher your loss to unproductive species will be. IOW at 25% reserve you can expect 20% of the species copmposition to be unproductive. AT 12% reserve 40% of the species will be unproductive. No reserve and 60% of the species will be unproductive.
You then need to allow another 50% to allow for sustainence during seasonal deficits.
Then you need to allow at least another 10% of the biomass being phsyically unavailable because it’s been trampled, is too far from water, been burned and so forth.
Then you need to allow that 10-30% of your animal biomass is going tobe lost to disease or predation.
IOW less than 10% of the theoretically available biomass will be actually available to your large beastie.
Then you take your calculations from there and start assuming your optimistic 10% conversion efficency of plant to animal biomass.
More reasonably you’d just look at actual stocking rates which work out about 10ha/tonne and use that as the absolute maximum baseline.
OK, so based on the response currently available, I sat down and chose some species following your herbivore guildlines of “nothing over 20 tons”. Now, let’s see what you think about what I’ve done. You’ll be proud to see I avoided famous dinosaurs like Triceratops in favor of less known but smaller dinos.
A few notes: Since these dinosaurs have lived on the island for 65 million years, and they had grasses for much of that, I’ll assume they can indeed digest grass, although many of the creatures have been dead long before grasses came around. In addition, I making lots of stuff up (like Camarasaurus having a good sense of smell.) This is intended as speculation, and while realism reports are welcome, I am not inclined to start a fiery debate.
Finally, these are only some of the dinosaurs who live on the island, but the most common. While they don’t show a complete food chain, these are the main dinosaurs who will somehow fit with the plot.
Now! The herbivores and omnivores:
Ankylosaurus
Behavior: Slow-moving, heavily defensible, lone creatures. They roam around in large areas, with the males each having their own territory, and the females roaming in between. After laying eggs, females will stay in the young’s father’s territory, as adult males will kill young other then their own.
Camarasaurus
Behavior: Living in groups of three or four adults of mixed gender plus young, Camarasaurus will join herds of other animals. Like modern Baboons and Ibex in the highlands of Africa, the Camarasaurus use their sense of smell to complement the other animals, who may have good sight, or hearing.
Compsognathus
Behavior: Living in huge herds of 50 or more, these small dinosaurs follow larger animals for protection while hunting small lizards, rats, and other small animals. They also eat from dead animals before larger predators show up. In addition to this, Compsognathus will also eat berries, small fruit, and other meaty plants.
Prenocephale
Behavior: Like modern bighorn sheep, these creatures frequent the mountains and hills of the island. While they butt heads for dominance, they are too small to threaten most predators, and instead run away.
Iguanodon
Behavior: These Iguanodon are smaller then average, only reaching about two tons. They are quite aggressive, however, akin to modern buffalo. They graze in medium herds away from other herbivores, and will stampede predators and herbivores alike when provoked.
Kentrosaurus
Behavior: Kentrosaurus on this island come in two varieties, the average Kentrosaurus and the Dwarf Kentrosaurus. The larger version lives out on the plains and is usually a peaceful grazer, joining mixed herds and assuming defensive positions only when predators are near. The dwarf variety, which lives in the jungles, is very different. Extremely aggressive when even slightly provoked, these creatures are feared and avoided by any other jungle creature.
Maiasaura
Behavior: The Maiasaura live in huge groups numbering hundreds throughout the island. Each group has a large nesting ground somewhere on the island, and returns there in the dry season to lay eggs, who hatch by the wet season. The normally slow and docile creatures become ferocious during the nesting season, attacking and even killing though sheer numbers almost any of the predators that frequent the island.
Lambeosaurus
Behavior: These giant herbivores reach 50 feet quite regularly, and are one of the larger subspecies of Lambeosaurus. These creatures are brightly colored with a thundering cry, and live in large mixed herds. Small, usually docile animals become far more active around Lambeosaurus, as their large size and rather defensive nature is enough to deter many predators, and their excellent hearing allows them to sense those who still approach. Their thundering alarm bellow can sound for over a mile, and other animals have come to recognize these as danger warnings. Many predators have been seen to abandon a hunt when a Lambeosaurus alerted their intended target.
Pachycephalosaurus
Behavior: Pachycephalosaurus are docile grazing animals. They live in dedicated herds, and avoid other herbivores. They are usually more inclined to run then fight. Their herds are extremely tight nit, however, and if a predator catches one of their number, the entire group will charge against even hopeless odds, trying to rescue their herd-mate.
Styracosaurus
Behavior: Styracosaurus are usually separated from other dinosaurs, living in small family groups of one male, a female or two, and young. Once the young reach maturity, they are cached away. This is one of the only instances of inter-species violence, however. Males find unrelated females, and once a group is formed, it never breaks. When two groups meet, they mingle, eat together, and then separate cleanly and with no fights. Males and females who cannot find a female will usually join mixed herds for protection until they meet one another. And interesting tidbit is that only about 1 in 3 Styracosaurus is a male. This ensures that every male can find at least one mate.
Therizinosaurus
Behavior: These large animals live in small groups of seven or eight adults. Male/female distribution in these groups is even, and an alpha female leads the group to food, water, and nesting sites. These animal’s large claws are used for display by males, shredding foliage for easy consumption by young by females, and defense by all.
Well, what do you think? Am I missing any important niches that aren’t filled by small modern animals like rats and lizards? Predators coming soon!
Honestly, you might be better off making up your own dino names for this. Essentially, a Camarsaurus (for example) that evolved alongside grass and consumes it regularly isn’t really a Camarasaurus. It can, perhaps, be a descendant, of course, but it would necessarily be a fundamentally different animal. So I (as a reader) would accept “Camarasaur”, but not “Camarasaurus”.
Alright. Criticism accepted whole-heartedly. If the story called for actual dinosaur names, the I’d go by your route and name them by their genus or family rather then species. However, the story isn’t taking place in modern times; we haven’t completely decided yet, but we’re probably going Medieval/Early Renaissance. So all names will be nicknames. Dinosaur names are only for my (and the other author’s) convenience.
Harry Harrison did it West of Eden - Wikipedia Evolution continues, dinosaurs now would bear no more resemblance to dinosaurs then than we do to mammals then - and that is always the flaw.
If I’m writing a story in which dinosaurs are alive in nearly modern times, I think we can establish that evolution, although not Ecology or other sciences, sits down and shuts up.
Check Harrison out then because evolution does not shut up for him, but in fact goes the other way with genetic engineering replacing technology (being cold-blooded, his dinosaurs never used fire and had millions of years to breed frogs into microscopes)
First off-sorry if I offended you with the “Evolution has obviously shut up and sat down” thing. It’s a reference.
Now, as too the dinosaurs evolving: Yes, it makes more sense. But it’s not the feel I’m going for here. I’m going for a Jurassic Park-style horror survival story, set in the middle ages, with dinosaurs that the average reader could, with a bit of research, recognize. This can be a sort of “mini game” in the story: Try to figure out what each dinosaur is. Evolution is just not what I’m going for here.
While I think your savannah comments are spot-on, I disagree with this assessment. His desert construction sounds very much like Hawaii (the Big Island). The hottest and driest part is the east-northeast portion of the island. North Kohala gets less than 5 inches of rain per year. The uplands (Waimea) have a great-plains-style grassland. He just has to cut his 45km in half. And he has to keep in mind that his volcanoes, while providing the rain shadow needed, are going to take up a LOT of precious biomass real estate. Much of the interior of the Big Island is very high, and very desolate.
I’d say that’s pretty good job. A couple of points though.
Firstly you seem to be lacking the mid sized herbivores. There are no animals in the human-cat size range, and that’s very odd. In a real system you expect to have a continuous size distribution from elephants down to mice. What you’ve described is akin to a system that has elephants and antelope, but no rabbits or rats. What’s occupying the niche of the kangaroos or springbok?
Secondly, what about the juveniles? Especially for the larger herbvores it’s unllikely that the juveniles lived alongside the adults, the size discrepancy was too large. It would be like having a cow trying to take care of a rat sized calf. To much chance of being trod on and too hard to look for predators over such a huge size range. So have you given any thought to where are the juveniles living, and how?
Actually while Harrison is a good read it’s lousy science. Dinosaurs existed in essentially the same forms and occupying essentially the same niches for over 100 million years. There’s absolutely no reason to believe they would have changed suddenly in the last 60 millon years
Dinosaurs now, 60 million years later, would bear at least as much resemblance to dinosaurs then as the ones then did to dinosaurs 120 million years earlier.
I was assuming that the dinosaurs would raise their children to a certain size, then the young would leave. I suppose they could leave the eggs behind, and the young catch up later, however.
As for smaller dinosaurs: Compsognathus is very small, and Prenocephale is 8 foot long, but weighed only 130 kilos-like a human. However, you are right. More, smaller dinosaurs coming up soon. Protoceratops fits the bill? Dryosaurus? Any more suggestions for stuff that’s SMALLER then that? I can’t really find many herbivorous dinosaurs smaller then Dryosaurus… I know they are there, though.
It’s unlikely that the large herbivores would care for the young simply because of the size discrepancy. It’s more likely that they, and probably all dinos, followed a pattern similar to crocodiles or megapodes, with parents watching the nest and then abandoning the young shortly after hatching. The exact lifestyle of the young is unknown, but it’s hard to imagine how a slow moving, dog sized herbivore would survive in open areas. Similarly the behaviour of crocs and monitors suggets that so the young carnivores also would have had to hide. So likely they formed creches of similar age individuals that inhabited forests, marshes or similar areas where they could find shelter form the larger predators.
I really don’t know enough to give any suggestions, but at least some of that niche was likely occupied by non-dinos such as turtles or iguanas.
First off North Kohala is the NNW most extremity of the island. By no stretch is it east of anywhere.
Secondly according to everyrainfallmap I’ve ever seen, the east northeast region gets 70-140 inches annually. The driest areas are all in the west, directly behind the peaks. Hawaii’s winds are predominantly from the NNE, and as a result the dry parts of North Kohala itself lie directly behindThe Kohala peak
All this sits perfectly with what I said above: to get an arid area on as island you need a significant area of highlands to produce as a rain shadow, and the area immediately behind that rain shadow will be the driest point, rather than the 45km adjacent to the ocean. Hawaii in general and North Kohala in particular fits this pattern perfectly. The most arid regions of both the island generally and North Kohala specifically are those portions are those that are immediately leeward of a peak and.
No, in order to get the driest area within 45 km of the coast he needs to have his highest peak within 45 km of the coast. Doesn’t matter what else he does, barring some contrived confluence of geography the driest areas are going to be immediately leeward of the peak, just as they are in Hawaii.
You’re right, but I think you’re overrating the humidifying power of the ocean. In the rain shadow, Hawaii is quite dry right up to the beach. (That’s one reason the resorts are up there in the NNW. Few rainy days.)
Yes, the land immediately leeward of the peak will be driest. But for a good distance out, the land can still be quite dry.
On a tighter re-read of the OP, I think we’re fighting over the wrong things here. I read his post as meaning, “I want to have desert to the one side of the mountains.” No problem. Not as “I need it to be lush in the mountains’ rain shadow and drier and drier further out toward the coast.” Problem. Reverse that progression, and he’s fine. Or shove the mountains a bit further east, so the rain shadow falls on the entire coast–then it’s all desert on that side.
That is only true where the peak is within 10 miles of the coast. IOW where the coast is in the raindhsaow immediately leeward of the peak. For those peaks more distant from the coast the map clearly shows that the driest area is within 5 miles of the peak, and that it becomes increasingly wet as it approaches the coast. And this applies to the whole world, not just Hawaii.
So I repeat what i said above: The only way to have the driest area within 45 km of the coast is to have the highest peaks within 45 kmof the coast.
Sure, like the Atacama desert. But the driest area isn’t going to be within 45 km of the coast if the high point is more than 45 km from the coast.
It’s also nothing whatsoever like the description given, where “After you cross the midpoint of the island, it starts getting warmer and dryer, with the final third being more like the dry savanna, with the final 30 miles or so being a hot desert.”
What you are describing is a situation where after you cross the midpoint of the island, it abruptly becomes warm and dry with 30 miles or so being a hot desert that gradually becomes colder and wetter producing a more mesic dry savanna, with the final 30 miles or so being comparitively wet.
